The NSW state-wide marine debris threat and risk assessment identified microplastics as a significant and emerging issue for the marine estate and a threat to its social and environmental assets. Consequently, addressing microplastic contamination is an emerging priority for government and natural resource managers. A key impediment to effective management of microplastic contamination relates to a lack of data on the distribution, abundance, and source of microplastics. This study addresses some of these identified knowledge gaps by assessing microplastics in estuaries and coastal outflows during flood and baseflow conditions. During the 2022 floods, we sampled microplastics from greater Sydney estuaries, two kilometres inside each estuary and two kilometres offshore, and compared this data to baseflow conditions (salinity 35). During baseflow conditions, microplastic variety and density in ocean surface waters are lower than in estuarine, whilst during flood conditions they are similar. Post floods, higher numbers of microplastics were found in both estuarine and marine waters, with evidence of catchment-sourced microplastics, such as artificial turf, present offshore. Overall, preliminary results suggest that in dry conditions microplastics coming from terrestrial sources remain within the estuary, whilst in wet conditions estuarine outflows are a significant source of microplastics to NSW ocean waters.